1. Field of the Invention
The present invention relates to a method of fabricating a near field optical probe employed to a near field scanning optical microscopy and near field information storage device and, more specifically, to a method of fabricating a near-field optical probe in which a cantilever and an optical tip are provided in one body and the optical tip is arranged to face the upper portion of the substrate.
2. Discussion of Related Art
After an atomic force microscopy was invented, a research has been widely conducted on applications of a scanning probe microscopy (SPM) capable of measuring optical, electrical, and magnetic characteristics of a sample in a nanometer resolution. The atomic force microscopy is supported by a cantilever and has a sharp tip of several nanometers. For a near-field scanning optical microscopy, the near-field light is output from the end of the tip made of a material transparent to the wavelength of the incident light to transmit the light, so that the optical characteristics of a sample can be checked through an interaction between the near-field light and the sample.
A cantilever-type near-field optical probe is mainly fabricated with the silicon substrate, and is classified into two structures according to a shape of the tip, i.e., a structure where the tip faces up in the direction perpendicular to the substrate and a structure where the tip faces down in the direction perpendicular to the substrate.
An example of a near-field optical probe having the structure where the tip faces down will now be described with reference to FIGS. 1A and 1B.
Referring to FIG. 1A, a groove in a reverse pyramid is formed on a silicon substrate 1 of the portion where a probe is to be formed, by using an anisotropic etching characteristic according to an orientation of the silicon, and then, a silicon oxide layer 2 and a metal layer 3 are formed all over the surface.
Referring to FIG. 1B, when a back side of the silicon substrate 1 is etched by using a predetermined mask until the metal layer 3 of the probe is exposed, a cantilever made of the thin silicon substrate 1 and a probe made of the silicon oxide layer 2 at the end of the cantilever are formed. Here, the silicon substrate 1 of the other end of the cantilever is not etched, thereby serving as a supporting frame. Next, the metal layer 3 is removed to form a hole 4 at the center of the probe, and a metal 5 is deposited at the backside of the cantilever and the probe to block light the transmission of light.
As another example, it is proposed that the optical tip is made of the silicon oxide layer, and the cantilever is made of the silicon nitride layer and the silicon oxide layer. [S. S. Choi et al., “Fabrication of subwavelength-size aperture for a near-field optical probe using various microfabrication procedures”, J. Vac. Sci. Technol. B. Vol. 21(1), p.p. 118-122, 2003]. In this method, silicon inside the optical tip is first etched, and an oxide layer is deposited. Here, a thick silicon oxide layer is grown in (111) direction due to the difference of growth rate of the oxide layer based on the orientation of the silicon. By using the silicon oxide layer as a mask, the hole of the optical tip is fabricated through an anisotropic plasma etching and an isotropic etching using HF.
However, the near-field probes having the arrangement described above has a chance that the substrate supporting the cantilever and the sample may be collided when the cantilever is moved and the probe is close to the sample.
Further, the near-field probe having a face-up tip can be fabricated in two methods. One method is to couple the cantilever and the tip, fabricated on the different substrates, respectively [Yasuhiro Shimada et al., “Probe with tip having micro aperture for detecting or irradiating light, near-field optical microscope, recording/reproduction apparatus using the probe, and method of fabricating the probe”, U.S. Pat. No. 6,201,226, 2001 Mar 13]. In this case, a process of arranging and aligning the tip and the cantilever is further required, which accompanies the difficulty in the process.
The other method is to fabricate the outer shape of the tip by etching the surface of the silicon substrate, and then, etch the backside of the silicon substrate to fabricate cantilever and remove the silicon inside the tip [P. Grabiec et al., “SNOM/AFM microprobe integrated with piezoresistive cantilever beam for multifunctional surface analysis”, Microelectronic Engineering, Vol. 61-62, p.p. 981-986, 2002Jul. 9. ]. In case that the near-field probe is fabricated in this method, the substrate supporting the cantilever and the sample is not collided when the probe is close to the sample. However, there is a difficulty in etching the silicon inside the tip or boring the hole of the tip. In other words, though it is necessary to maintain a constant thickness of the substrate during the silicon process, there is a difficulty in proceeding the process since the backside of the tip should be patterned after the most portion of the backside of the substrate is removed to form the cantilever. Further, with a focused ion beam (FIB), the hole of tip can be accurately bored. However, in this case, the high-cost apparatus is required.
In case that the near-field optical probe is used in the optical information storage device, the optical recording is enabled only when the transmittance of the near-field light transmitted from the end of the probe is high. With respect to this, researches have been made on improvement of the transmittance by fabricating a parabolic-type tip end using a bird's beak [K. Song et al., “Fabrication of a high-throughput cantilever-style aperture tip by the use of the bird's beak effect”, Jpn. J. Appl. Phys., Vol. 42, Part 1, No. 7A, p.p. 4353-4356, 2003 July. ].
Recently, a research was conducted over a method of fabricating the probe using an optical fiber. In the method, the optical fiber is dangled such that a width of an end of the optical fiber is several nanometers. Using an interaction between the end of the optical fiber and the sample to maintain the close distance, a microscopic optical characteristic of the sample is checked by measuring the interaction between the sample and the near-field light emitted from the end of the optical fiber. However, with the probe comprising the optical fiber, the arrangement of the probe is mechanically weak, and it is difficult to fabricate the multiple probes.